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| | | Supreme Being
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Last Login: 6/26/2008 4:01:08 PM
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| | In areas with soft water, both ferric and alum have a tendency to drop the pH to levels that can cause other problems. They basically chew up the alkalinity pretty much. If you have to then nitrify, this can be a problem, and you may have to add another chemical to suceed. Some of the operators I know have gone to sodium aluminate, which is expensive, but actually adds alkalinity to the system. Alldepends upon your effluent limits, background characteristics of the water, and relative costs of chemicals in your area. |
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Forum Member
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Last Login: 8/30/2008 1:28:49 PM
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| | Andy, just picking up on discussion and would agree with last comment that sodium aluminate, which add's alkalinity, can be very useful if pH depression is a problem for you (but will likely be more expensive than ferric alone). To my experience ferric depresses pH the most, alum second most, ferrous third most (only works for P removal if aerated to ferric in the aeration tanks or aerated grit chamber), and then polyaluminum chloride (PAC). There's your range of typical P removing chemicals. Assume your influent P levels are not up in summer (not mentioned to date) and that you don't run higher TSS in summer (as P in TSS will add to total P in effluent of course). To my experience most plants do better in the summer not worse. Another thing you can try if your effluent limit is very low (say 0.3 mg/l or less) is dual point addition with one metal salt added at the aerated grit chamber ahead of primary treatment (not sure from your description if you have primary sed) followed by second smaller dosage to mixed liquor ahead of secondary. Or if you don't have primary tanks, since it appears you have filters you can add ferric as you're doing, possibly augmented by polymer, or substituing PAC for ferric which has elements of both metal salt and polymer coagulant properties, then if needed add a small PAC dose ahead of filters for additional reduction. At the end of the day combination of effectiveness and cost by trial and error will tell you what's best. Once again if you haver a very low standard looking at where you're missing target- effluent soluble P or total P, will help guide you in best corrective action ie. mix of chemicals and/strategies to get to you to target P level at the end of the day. Chemical vendors may help you with some testing and contacting them for help is always a good idea. Wiff Peterson
Wiff Peterson |
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| | | Junior Member
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Last Login: 2/1/2008 6:26:27 AM
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| | You can expect a 35% increase in sludge production if you are adding the optimum dose of iron. Regards Grant H , Australia |
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| | | Forum Newbie
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Last Login: 2/23/2008 4:18:30 PM
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| hi all,
i'm new to this forum but have had experience using PAC (polyaluminate chloride) for phosphorus removal with small wastewater plant in southern rockies. have used it for over 6 years and feed it into our first (of five) basin(s) which has been converted to an anoxic basin with a submersible mixer. our influent is introduced at the front of the 1st basin along with our RAS from our clarifiers, and the selector return from our 4th basin. we drip the PAC into the RAS and INF zone and achieve < 0.1 mg/l consistently in our effluent. it is a bit more costly than ferric but not a pH depressant, most permits are 6-9 and most PAC has pH over 6.5 we feed soda ash to our first basin as alkalinity boost for nitrogen removal. a simple jar test can determine dosing rates.
good luck
highaltitude |
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